Gas burning apparatus



Feb. 16, 1937. c CARROLL r AL 2,070,969

GAS BURNING APPARATUS Filed May 10, 1932 2 Sheets-Sheet 1 [N VENTORd 67,446. f. CARAPOLL M4 Feb. 16, 1937. c. F. CARROLL ET AL 2,070,969

GAS BURNING APPARATU S Filed May 10, 1932 2 Sheets-Shet 2 Ca F7: PIRAW.

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)1 Mag @6- Patented Feb. 16, 1937 PATENT OFFICE GAS BURNING APPARATUS Charles F. Carroll and Arthur 0. Willey, Cleveland, Ohio, assignors to A. R. Carroll and J. L. Frantz, both of Cleveland, Ohio Application May 19, 1932, Serial No. 610,330

16 Claims.

This invention relates to gas burning apparatus and has for its object the provision of improved mechanism for producing a smokeless and noiseless gas flame of maximum heatingv effect under all circumstances, and with compensatory provisions for enabling the successful use of the apparatus with gases of widely varying heating value; the provision of a reliable, efficient, noiseless and smokeless gas burner which can be set accurately for any quality of gas substantially regardless of the gas pressure; the provision of a gas burning apparatus which can be adjusted for difierent capacities of burner substantially without altering the proportion of gas and air; while further objects and advantages of the in.- vention will become apparent as the description proceeds.

Our improved burner is designed especially for use in connection with domestic heating units although it is usable wherever gas is burned for heating or power purposes. The quality of gas obtainable in different localities varies all the way from perhaps 1400 B. t. u. per cubic foot of gas (which is an extremely high figure found sometimes in natural gas) down to 310 for water gas, 120 for producer gas and less than 100 for blast furnace gas. Public service corporations in most localities are required by ordinace to maintain the quality of their product within a certain specilied range of B. t. u. per cubic foot but even this varies considerably in different parts of the country, with the result that no one setting of gas-air ratio is usable everywhere, and furthermore the setting of the gas and air-intake ports further depends upon the gas-pressure employed when, as has usually been the case, the pressure of the gas has been relied upon to inspirate the necessary air after the manner of the Bunsen burner.

As a consequence of these various considerations the adjustment of a gas burner has been practically a matter of luck, yet to the proper adjustment of the gas and air mixture is chiefly attributable the economy or lack of economy of gas-heating.

According to this invention two separate and distinct adjustments are made, one, for the amount of combustible mixture to be consumed (dependent upon the size of the burner, the amount of heat desired, etc.) and second, an adjustment based solely upon the B. t. u. equivalent of the gas; these two adjustments serving at all times to produce a quiet and economical flame, thereby enabling one and the same gas burning equipment to be sent anywhere, installed by any steam fitter, and employed by any user with complete confidence of success. Furthermore by the employment of a particular type of metering device for the gas in combination with a particular type of pressure producing device for the air the apparatus is rendered self compensating throughout a wide range of conditions. i

In the drawings accompanying and forming a part of this application we have shown certain illustrative embodiments of our inventive idea. Fig. 1 is a perspective view of our improvement in one of its simplest forms; Figs. 2 and 3 are sectional views corresponding to the lines 2-2 and 3-3 respectively of Fig. 1; Fig. 4 is a perspective view of a diaphragm plate used in each form of our invention; Fig. 5 is a perspective View of a second embodiment of our invention involving additional correlated features; Fig. 6 is a sectional view through one of the diaphragm valves shown in Fig. 5; Fig. '7 is a sectional View corresponding to the line l'--'l in Fig. 5; Fig. 8 is a sectional view corresponding to the line 8-8 in Fig. 5; Fig. 9 is a fan-characteristic curve; and Fig. 10 illustrates our improvements in a yet simpler embodiment.

Describing by reference characters the parts shown in these drawings and first having reference to Figs. 1, 2 and 3, the burner i may be of any suitable or desired form according to the desire of the manufacturer or the whim of the user. It usually comprises some kind of a distributing chamber-2, an inlet pipe 3 of some kind which by its length and size determines a certain amount of limitation to the amount of combustia ble mixture which can be supplied to the burner, and this amount can be further controlled, if de- 35 sired, by suitable metering means such as an orifice-place 4 located at some suitable point such as that indicated in Fig. 2 and having therein an orifice 5 of a size determined by the number of cubic feet of combustible mixture required to be burned per hour.

The air employed with this burner is furnished by a suitable pumping-device, such as the centrifugal-fan indicated generally at 6 and driven by a suitable electric motor 1. This pumpingdevice is chosen to have a fairly straight-line relation of pressure to volume throughout the range employed, as shown graphically in Fig. 9, wherein abscissae represent volume in cubic feet per hour and ordinates represent pressure in inches of water. This relation is most easily obtained by the use of a centrifugal fan of high slippage, although in Fig. 10 we have shown an aspirator or Venturi-tube type of pumping device which is also usable. A centrifugal fan of this nature is shown in Figs. 1 and 2 and comprises a hollow casing 8 having a peripheral discharge neck 9 and an axial inlet opening ID with which is concentrically mounted a bladed rotor I! mounted directly on the shaft ii of the motor 1. A very small inexpensive motor is all that is required, and the small amount of electricity employed to operate this fan is more than compensated by the economy of gas and regulation of operation secured by its means.

Between the fan-outlet and burner-inlet is loc-ated a side branch connection by which combustible gas is supplied by way of a metering device which when once set to produce a combustible mixture in accordance with the heating value of the gas continues to furnish such an amount of gas as to produce a substantially uniform mixture regardless of the amount of such mixture allowed to pass into the burner throughout a wide range. In these drawings we have shown a casing it having therein a recess l4 constituting a mixing chamber and connected at opposite ends to the burner and pumping device respectively. Formed in this casing and communicating with the mixing chamber at one side is an inlet port l5 of considerable size, and located in line with this port is a gas-supply connection It also of substantial internal diameter. Located between this connection and port is a metering disk of a type whereby the amount of gas can be accurately predicted and automatically maintained at a determined proportion to the amount of air throughout a wide range of mixture-quantities. So far as we have been able to discover this can be effected only by the particular type of metering device now to be described, for the reason that no other type separates the effect of pressure from that of area of opening. The construction and mode of operation of our improved gas burning apparatus is based upon certain well known fundamental propositions in hydraulics but applied in a new y,

It is well known that where Q represents the total volume flow of any fluid, V represents the velocity and A represents the cross-sectional area of the stream. It is also well known that wherein g is the acceleration of gravity, h is the effective pressure (1. e. the difference of pressure at the two points between which the flow occurs given in terms of head of the fluid) and C is the coefficient of discharge, which depends upon the type of aperture but is definite for any given orifice. C is dependent upon the shape (both transverse and longitudinal) of the orifice, the surface smoothness, the density, viscosity, and compressibility of the fluid. As between different combustible gases the difierence in density and viscosity can be neglected, as can also the compressibility at the small pressures employed; and in the case of apertures in flat plates this coefficient is substantially a constant in case the apertures are all circular and the surfaces and edges are similarly smoothed. The nearest approach to constancy is attained when the plate is made thin (especially under commercial conditions) but changes in the thickness of the plate are of less importance than the shape of the aperture and the nature of the approach thereto in both directions.

Hence Q=AV may be written But 6.3 C is now a constant which can be represented by K s0 Hence Under these particular conditions, therefore, the quantity of the gas flowing into the mixer depends solely upon the diameter (d) of the opening 20 and the square root of the difierence in gas-pressure (p1p2) at the opposite sides of this opening which causes the flow. If the pressure 101 in the gas main is constant the quantity of gas flowing into the mixing chamber depends only upon the pressure 122 inside the mixing chamber. The simple and reliable relations herein described are not present in the case of non-circular orifices or if their edges be other than sharp. Only by paying strict care to the size, shape, and character of the opening is it possible to control the flow of gas with accuracy, but when this is done, it then becomes possible to adjust the apparatus so that the consequent pressure efiect becomes selfactive to maintain a substantially fixed relative proportion between the components of the mixture throughout a practical operating range.

To utilize this relationship we interpose between the gas-supply connection I6 and the port I 5 a flow-meter of the particular type called for by the above equations, namely a plate l9 preferably of very thin metal (or similar rigid material) having a perfectly circular, smooth-edged aperture 20 registering with the port l5, and sufficiently smaller than the port 15 and pipe l6 so that neither of these shall have any substantial throttling effect upon the fluid flow. This plate is clamped in place by a back-plate 2| screwed to the casing and having the pipe I6 screwed thereto. In Figs. 3 and 8 the plate I9 is carried by 'a rotatable spindle I? mounted in a bore formed in the casing l3 and furnished with a knob [8 by which it can be turned so as to bring into register any one of several orifices of graduated size with which the plate is formed, and also furnished with a pointer 22 moving over a scale 23 by which the position of the plate is indicated. This enables the flow-meter to be set for gases of different heating value, or for burners of widely difiering capacities or pumping devices of widely dissimilar characteristics. In case the same pumping device be always employed and in a locality of uniform gas value, one setting of the metering device will serve throughout a Wide range of burner capacities as we will soon show, and in such cases it is enough to use merely a stationary plate I90. clamped in place and having therein a single aperture of proper size, shape, character, and position.

The tube i6 is preferably connected to the gas-main 24 by means of a pressure-reducing valve A which in its preferred form comprises an apertured partition 25 located between the tube It and main 24 and cooperating with a valve-member 26 carried by a stem 2'! which is attached to a flexible diaphragm 2B normally held open by a spring 29 on which presses the adjusting screw 30. The diaphragm being acted upon by the pressure in the tube It, any excess of pressure therein serves to close the valve 26 against the tension of the spring 29. The opposite face of the diaphragm is open to atmospheric pressure by way of a vent-aperture 33.

The use of a pressure-reducing valve is not always necessary. In case the utility company maintains the gas at a fairly uniform pressure, and the basic formula above given shows that small changes in pressure are not particularly important since pressure is only effective proportionally to its square root) and the pumping device be adjusted to produce a maximum pressure which is only slightly lower than that of the gas, the apparatus is operative without any separate reducing valve; but owing to the wide variations in pressure exhibited in most gas mains we prefer to employ a pressure reducing valve adjusted to a pressure Which is below any pressure ever reached by the gas supply, thus rendering the apparatus independent of pressure variation. For example the fan shown in Figs. 1 and 2 produces the pressures shown in Fig. 9, (e. g. .9 inch of water at 2500 cubic feet per hour) and the reducing valve A is adjusted to give a pressure of 3% inches of water (equivalent of 2 oz. per square inch) and the resulting mixture produces quiet perfect combustion. If the mixture flow be restricted by using a smaller burner, or by constricting the throats of the burner as by a plate i, or by the use of a valve 35 of any type, the increased pressure inside the mixing chamber reduces the flow of gas through the orifice 2b in such proportion that the composition of the mixture remains substantially uniform throughout a considerable range of mixture quantities. This. is due to the fact that upon any obstruction of the fan outflow the pressure is increased and proportionally restricts the gas inflow, while upon the removal of any existing restrictions the pressure falls proportionately to the increase in the quantity passing through the burner allowing a proportionately increased inflow of gas.

It would be possible, with the use of orifice meters of the type herein shown to list in advance the sizes of orifices required for various qualities of gas, pressures of gas, pressures of air, quantities of mixture, etc., but owing to the fact that each of these quantities is a variable the total number of possible conditions is very great. As an example of one setting, however, using the fan and orifice-meter heretofore described, with gas of 1140 B. t. u. per cubic foot, and at a pressure of 2 ounces per square inch (3% inches of water) the size of the gas aperture was 3-32 inch. Merely by changing the sizes of the orifices leading to the burner the amounts of gas admitted into the mixing chamber were varied as follows:

Diameter of mixture Cubic feet orifice of gas Inches ployed for the gas throughout, the composition of the mixture remaining within permissible limits. It will be remembered that the amount of mixture flowing to the burner depends not only upon the size of the orifice but also upon the pressure produced by the fan and this pressure varies with the volume allowed to be delivered as shown by Fig. 9. By changing the adjustment of the pressurereducing valve A the rate of gas flow can be made either more or less responsive to changes of the pressure in the mixing chamber, being rendered less responsive as the gas pressure is increased and more responsive as it is decreased. Likewise by using a gas of proportionately increased B. t. u. content, the larger burner or the larger flame can be supplied through a smaller orifice, the apparatus still exhibiting the described automatic compensating features. For gases of different heating value the area of the orifice (other things being unaltered) varies inversely with changes in the B. t. u. content.

The range of automatic control can be increased by the employment of a by-pass tube 35 leading from the fan-outlet to the interior of the reducing-valve as shown in Figs. 1 and 3. As a consequence of this connection, whenever the pressure in the fan-outlet is increased by a corn striction between it and the burner, some of this increased pressure is conveyed to the diaphra 3.1 28 and is operative to close the valve 26, this being in addition to the back-pressure effect inside the mixing chamber 14 and operating at the aperture 29. The size of the pipe 3! is of some importance in this connection, this being indicated graphically by the provision of an adjusting valve 32. If the facility of communication from the fan outlet to the diaphragm should become too great the gaspressure would be unduly reduced at all times. It will be noted that the pressure to be delivered by the fan must always be less than that for which the reducing-valve is adjusted, although the two must be of the same degree of magnitude in order to permit the automatic compensation heretofore described. The effect produced by way of this connection 3! is'usually of secondary importance throughout the narrow range within which any such device is employed but serves to extend the range beyond that wherein the upstream pressure is alone sufiicient to maintain constant the proportion of gas to air.

In Fig. 5 we have shown two further refinements which may be used either separately or simultaneo'usly. The first of these is the employment in connection with the burner pipe 3* of a quantity valve 35 mounted directly at one end of the valve casing lB and consisting of a circular disk 3? carried by a rotating spindle 33 having a knob 3d and furnished with position indicating means suitably graduated. The diaphragm is formed with apertures 42 of graded size adapted to be brought one at a time into line with the connection 3 thus enabling the user to adjust the flame in accordance with accurately determined requirements. The knob l8 and adjusting disk iii are shown as before, although it is in some cases desirable to employ a less conveniently varied type of quality adjustment, since the gasquality is little subject to change and the apparatus is usually adjusted for this once for all by the expert who installs the outfit.

In Figs. 5 and 6 we have shown a further refinement including a diaphragm valve and thermostat control, all operating through one and the same motor. Two diaphragm valves are employed, that at A being identical with that shown in Figs. 1 and 3 and functioning as a gas pressure controller, and that shown at B being located in series with the valve A, but arranged slightly differently inside, namely: the valve 26 (Fig. 6) closes in the same direction as before and is connected to a stem 2'! which is connected to a diaphragm 28 but instead of a spring 29 tending to open the valve, this device is provided with a spring 45 tending to close the valve, this being done in the present instance by carrying the stem through the top of the casing and wrapping the spring 35 around it. A smaller diaphragm 46 serves to shield the diaphragm 28 from the effect of pressure inside the valve, and a pipe All communicates with the pipe 31 which leads from the fan-outlet. This pipe 3! may also, as shown in Fig. 5, be connected to the valve A in the same manner as shown in Figs. 1 and 3, or this feature may be omitted together with its function. In this case the chamber between the two diaphragms is vented to the outer air by way of an aperture 48.

An advantage of the arrangement just described is that it lends itself to a particularly convenient thermostatic operation. A heat-responsive member 50 supported in the apartment to be heated (assuming the device to be employed for domestic heating purposes) serves to control the connection of the motor I to the line wires 5| through suitable relays 52, 53. Whenever the motor 1 is energized it first sets up a current of air through the burner, and also creates a pressure on the diaphragm 28 of the valve B which opens that valve and thus permits the flow of gas into the burner so that the pilot flame (not shown) causes a quiet ignition; likewise whenever the circuit of electricity through the motor is arrested, the diaphragm-valve, being controlled by the same pressure which supplies mixture to the burner, reduces the gas-flow in such wise that the flame becomes extinguished quietly. Likewise the one motor which supplies mixture to the burner produces motive power for operating the valves.

In Fig. we have shown our improvements in their simplest and most rudimentary form. The pumping device here comprises an air jet nozzle 59 projecting into a Venturi tube 6|, this being another form of pumping device wherein pv c throughout some range. The metering orifice 2% for the gas is formed in a stationary disk, the quantity of mixture delivered to the burner is controlled by the butterfly valve 4 and the gas company is trusted to keep the gas pressure within reasonable bounds. Such a device is wholly operative and much superior to the usual type of burner.

When a centrifugal-fan is employed as a source of the air-pressure it is important that its inlet ill be left unobstructed atall times. Other devices can, however, be employed for producing and maintaining this air pressure provided al-' ways that they exhibit the specified not very exacting degree of constancy between pressure and volume throughout the range employed, and many other changes in detail can be made without departing from the scope of our invention, Wherefore we do not limit ourselves to the details herein described except as the same are specifically recited in our several claims which we desire may be construed each according to its own limitations and without reference to limitations contained in other claims.

Having thus described our invention what We claim is:

1. Gas burning apparatus comprising, in combination, a burner, an air-pumping device operatively connected to said burner, said pumping device being of a type exhibiting the relation, 110:0 throughout a substantial range of pressure, p, and flow of volumes, 2), 0 being substantially a constant, there being a mixing chamber located between said pumping device and said burner and having an inlet port in its wall exposed to the air pressure in said chamber, a gas connection communicating with said port and supplying gas thereto at a pressure greater than that within said mixing chamber, and a thin sheet of rigid material traversing said port and having therein a circular sharp edged aperture whose diameter is greater than the thickness of said sheet and whose margin is spaced from the wall of said port, whereby a substantially fixed gas-air ratio is maintained in the mixing chamber throughout the stated pressure ranges.

2. Gas burning apparatus comprising, a burner, an air-pumping device operatively connected to said burner, said pumping device being of a type exhibiting the relation, pvzc throughout a substantial range of pressure, p, and flow of volumes 2), 0 being substantially a constant, there being a mixing chamber located between said pumping device and said burner and having an inlet port in its wall exposed to the air pressure in said chamber, a gas connection communicating with said port and supplying gas thereto at a pressure greater than that within said mixing chamber, means located between said mixing chamber and burner for controlling the quantity of mixture admitted to the burner, and a flat sheet of rigid material traversing said port and having therein a circular sharp edged aperture whose diameter is greater than the thickness of said sheet and whose margin is spaced from the wall of said port whereby a substantially fixed gas-air ratio is maintained in the mixing chamber throughout the stated pressure ranges.

3. Gas burning apparatus comprising in combination, a burner, a hollow member connected thereto and constituting a mixing chamber for receiving air under pressure, said member having an air-inlet and a gas-inlet port of fixed area exposed to the air pressure of said chamber, a thin sheet of rigid material traversing said gasinlet port and having therein a circular sharp edged aperture whose diameter is greater than the thickness of said sheet and whose margin is spaced from the wall of said port, a centrifugal fan having its outlet connected to said air-inlet, and means for supplying gas to said port at a pressure which is greater than the highest pressure produced by said fan whereby a substantially fixed gas-air ratio is maintained in the mixing chamber for varying air pressures and flows so long as the product of such variables equals a constant.

4. Gas burning apparatus comprising in combination, a burner, a hollow member connected thereto and constituting a mixing chamber for receiving air under pressure, said member having an air-inlet and a gas-inlet port, an orifice meter of fixed area traversing said port and exposed on one side to the air pressure of said chamber, a gas-supply pipe for said port, an airsupply pipe for said air-inlet, and a pumping device for such air-supply, the gas supply pressure exceeding the air pressure in said mixing chamber whereby a substantially constant gasair ratio is maintained in the mixing chamber for varying air pressures and flows where the product of such variables equals a constant.

5. Gas burning apparatus comprising in combination, a burner, a hollow member connected thereto and constituting a mixing chamber for receiving air under pressure, said member having an air-inlet and a gas inlet port, an orifice meter of fixed area traversing said port and exposed on one side to the air pressure oi-said chamber, a gas-supply pipe for said port, an air-supply pipe forsaid air-inlet, a valve between said mixing chamber and burner, and an air-pumping device connected to said air-inlet, the gas supply pressure exceedingthe air pressure in said mixing chamber whereby asubstantially constant gas-air ratio is maintained in the mixing chamber for varying air pressures and flows where the product of such variables equals a constant.

6. Gas burning apparatus comprising, in com bination, a. burner, an air pumping device operatively connected to said burner, said pumping device being of a type exhibiting the relation pv=c throughout a substantial range of pressures, p, and fiow of volumes, 1). 0 being substantially a constant, means comprising a fixed orifice located between said pumping device and burner for supplying gas to the air delivered thereto by said pumping device in opposition to and in accord ance with the air pressure at the point of gas delivery, and a pressure-regulator controlling the supply of gas to said fixed orifice so set to a previously determined adjustment that the gaspressure is rendered constant and only slightly greater than the pressure produced by said pumping device, whereby a substantially fixed gas-air ratio is maintained in the mixing chamber throughout the'stated pressure ranges.

'7. Gas burning apparatus comprising in combination, a burner, an air-pumping device operatively connected to said burner, said pumping device being of a type exhibiting the relation po=c throughout a substantial range of pressures, p, and flow of volumes, 1;, 0 being substantially a constant, and means located between said pumping device and burner for supplying gas to the air delivered thereto by said pumping device comprising a pressure-regulator so set to a previously determined adjustment that the gas-pressure is rendered constant and only slightly greater than the pressure produced by said pumping device and a metering valve located between said pumping device and said pressure regulator, said valve com prising a thin plate having therein a series of circular apertures of varying sizes and means for bringing the difierent apertures selectively into register with said means whereby the B. t. u. value of the mixture of gas and air and the gasair ratio may be maintained constant.

8. Gas burning apparatus comprising in combination, a burner, an air-pumping device operatively connected to said burner, said pumping device being of a type exhibiting the relation po=c throughout a substantial range of pressures, p, and flow of volumes, 0, 0 being substantially a constant, gas conducting means comprising a fixed orifice located between said pumping device and burner for supplying gas to the air delivered thereto by said pumping device in opposition to and in accordance with the air pressure at said orifice, means for metering the combustible mixture entering said burner, and a pressure regulator in said gas conducting means ahead of said fixed orifice so set to a previously determined adjust-merit that the gas pressure is rendered constant and only slightly greater than the pressure produced by said pumping device whereby a substantially fixed gas-air ratio is maintained in the mixing chamber throughout the stated pressure ranges.

9. Gas burning apparatus comprising, in combination, a burner, an air-pumping device operatively connected to said burner, said pumping device being of a type exhibiting the relation pv=c throughout a substantial range of pressures, p, and flow of volumes, 2:, 0 being substantially a constant, gas conducting means located between said pumping device and burner for supplying gas to the delivered thereto by said pumping device, means for metering the combustible mixture entering said burner, a pressure regulator in said gas conducting means ahead of said metering means so set to previously determined adjustment that the gas pressure is rendered constant and only slightly greater than the pressure produced by said pumping device, and an adjustable metering valve of the fixed orifice type located between said pressure regulator and said means whereby the B. t. u, value of the mixture of gas and air and the gas-air ratio may be maintained constant.

10. In gas burning apparatus, in combination, a low pressure centrifugal blower, a burner, a hollow casing interposed between said burner and the outlet of said blower, a gas conducting sidebranch communicating with said casing, a gaspressure regulator connected to said side branch so set to a previously determined adjustment that the pressure of the gas is rendered constant and only slightly greater than the pressure produced by said blower, and an orifice-meter comprising a thin disk with an orifice therethrough located between said pressure regulator and the interior of said casing whereby a substantially fixed gas-air ratio is maintained in the mixing chamber for varying air pressures and fiows as long as the product of such variables equals a constant.

11. In gas burning apparatus, in combination, a low pressure centrifugal blower, said blower being of the type in which the product of pressure times volume equals a constant throughout a substantial range of pressures, a burner, a hollow casing interposed between said burner and the outlet of said blower, a circular recess at one side of said casing, a thin disk in said recess and having a plurality of circular apertures of graduated sizes arranged around its periphery, a sidebranch passageway communicating with said casing and located in the arc with said apertures, means for changing and indicating the position of said disk, a diaphragm valve under control of the air pressure at the outlet of said blower communicating with said side-branch passageway, and a source of gas supply connected to said valve whereby a substantially fixed gas-air ratio is maintained in said casing for varying air pressures and flows so long as the product of such variables equals a constant.

12. In gas burning apparatus, a controlling and mixing device comprising a hollow casing having a main passageway therethrough and also having a smaller side branch passageway, said casing having at one side of said passage a shallow circular recess which is intersected by said passageway, a thin disk in said recess having a plurality of circular apertures of graduated sizes arranged around its periphery in line with said passageway, a rotatable spindle journaled in said casing and having said disk attached thereto, means for rotating said spindle, means for indicating the position of said disk, means for supplying the main passageway of said casing with air under pressure, and means for supplying the branch passageway of said casing with gas at a pressure slightly exceeding the air pressure in the main passageway of said casing.

13. In gas burning apparatus, a controlling and mixing device comprising a hollow casing having two shallow circular recesses and two passageways, one passageway intersecting each recess and the two passageways communicating with each other, a disk in each recess, each disk having a plurality of circular apertures of graduated sizes arranged around its periphery and adapted as the disk is turned to register with the corresponding passageway, a rotatable spindle connected to each disk and journaled in said casing, and means for rotating the spindles and indicating the positions of the disks.

14. In gas burning apparatus, in combination, a burner, an air pumping device operatively connected to said burner in air supplying relation, a mixing chamber for receiving air from said pumping device located between said pumping device and burner, means for maintaining a; fixed gas-air ratio in said mixing chamber comprising a metering orifice exposed at one side to the air pressure in said mixing chamber and exposed at its other side to a source of gas supply at a substantially constant pressure which normally exceeds the air pressure in said mixing chamber, a shut-off valve for such gas, and fluid pressure means operatively connected to said valve and communicating with said pumping device whereby said valve is held open by the pressure of the air delivered by said pumping device and is caused to close whenever said pumping device is inactive.

15. In gas burning apparatus, in combination, a burner, a rotary air-pump having its outlet connected to said burner, an electric motor operatively connected to said air-pump, means for controlling the operation of said motor, a mixing chamber located between said pump and burner for receiving air under pressure from said pump, a gas pipe leading to said mixing chamber, means comprising a fixed orifice for maintaining a constant gas-air ratio in said mixing chamber, a normally closed valve in said gaspipe, a fluid-pressure device for opening said valve, and a connection from the pump-outlet to said fluid pressure device, said device operating at the pressure produced by said pump.

16. In a thermostatically controlled gas burning apparatus, in combination, a burner, an electrically operated air pumping device having its outlet connected to said burner, a conduit for connecting said pumping device and burner, a thermostat located in a position to be actuated by the heat produced by said burner and connected in controlling relation with respect to said airpumping device, means comprising a fixed orifice communicating with said conduit for supplying combustible gas to the air delivered by said pumping device and effective for maintaining a substantially fixed gas-air ratio in said conduit, a valve controlling the gas supply, and air pressure means communicating with the outlet of said pumping means and operatively connected to said valve whereby-said valve is held open while said pumping device is being operated and is allowed to close while said pumping device is idle.

CHAS. F. CARROLL. ARTHUR O. WILLEY. 

